Splash-saltation trajectories of soil particles under wind-driven rain

It is usually recognized that relatively large amounts of soil particles cannot be transported by raindrop splashes under windless rain. However, the splash-saltation process can cause net transportation in the prevailing wind direction since variations in splash-saltation trajectory due to the wind are expected in wind-driven rain. Therefore, determining the combined effect of rain and wind on the process should enable improvement of the estimation of erosion for any given prediction technique. This paper presents experimental data on the effects of slope aspect, slope gradient, and horizontal wind velocity on the splash-saltation trajectories of soil particles under wind-driven rain. In a wind tunnel facility equipped with a rainfall simulator, the rains driven by horizontal wind velocities of 6, 10, and 14 m s⁻¹ were allowed to impact three agricultural soils packed into 20×55 cm soil pans placed at both windward and leeward slopes of 7%, 15%, and 20%. Splash-saltation trajectories were measured by trapping the splashed particles at distances downwind on a 7-m uniform slope segment in the upslope and downslope directions, respectively, for windward and leeward slopes. Exponential decay curves were fitted for the mass distribution of splash-saltation sediment as a function of travel distance, and the average splash-saltation trajectory was derived from the average value of the fitted functions. The results demonstrated that the average trajectory of a raindrop-induced and wind-driven soil particle was substantially affected by the wind shear velocity, and it had the greatest correlation (r=0.96 for all data) with the shear velocity; however, neither slope aspect nor slope gradient significantly predicted the splash-saltation trajectory. More significantly, a statistical analysis conducted with nonlinear regression model of C₁(u_*²/g) showed that average trajectory of splash saltation was approximately three times greater than that of typical saltating sand grain.     

Effect of attachment configuration on the trapping efficiency of Vaseline-coated slide catchers for windblown particles

There are various types of the windblown sediment traps developed for wind tunnel and field studies. One of the main supports expected from these traps is in measuring surface dust concentrations to appropriately derive flux equations. The measurement performance and accuracy of a trap is very important and depends strictly upon the physical characteristics and the behaviors of dust grains with air flows. This paper presents the measurement results of static pressure distribution (SPD) of wind flow around Vaseline-coated slide (VCS) catchers with an aim of finding out whether or not particle trapping efficiency (η) of the VCS is related to the SPD. The SPD was evaluated by a wind reduction coefficient (R _c) in a series of wind tunnel experiments with different VCS settings which have different attachment configurations on a pole. Three VCS configurations were considered: a configuration on a circular plastic pole (CPP) and two configurations on wooden square poles (WSP₁ and WSP₂, respectively). Thus, the primary contribution of this work was to experimentally analyze the effect of the different attachment configurations on the SPD, and the secondary objective was to determine the effect of the SPD on the η. It was shown that spatial correlation and spatial pattern of the R _c were different in the surrounding area of each configuration, and ANOVA and DUNCAN tests indicated that η(s) of WSP₁, WSP₂, and CPP were different at the significant level of P ≤ 0.05 with the mean of 0.94 ± 0.09, 0.63 ± 0.14, and 1.13 ± 0.07, respectively. Additionally, the amount of PM₂₀, PM₄₀, PM₆₀, PM₈₀, and PM₁₀₀ trapped by the configurations of WSP₁, WSP₂, and CPP considerably varied depending upon the particular aerodynamic circumstances associated with every configuration.     

Splash detachment of sand particles under varying contact stress field of wind-driven raindrop impact

The effects of wind-driven rain (WDR) on sand detachment were studied under various raindrop obliquities. Results suggested a significant reduction in compressive stress on sand surfaces for a two-dimensional experimental set-up in a wind tunnel. During experiments, sand particles in splash cups were exposed to both wind-free rain (WFR) and WDR driven by horizontal winds of 6.4, 8.9 and 12.8 m s⁻¹ and rainfall intensities of 50, 60, 75 and 90-mm h⁻¹ to assess the sand detachment rate (D, in g m⁻² s⁻¹). The effects of sand moisture state (dry and wet) on the detachment of different-sized particles (0.20–0.50 and 0.50–2.00 mm, respectively) were also tested. Factorial analysis of variance showed that shear and compressive stress components evaluated by horizontal and vertical kinetic energy flux terms (KE_x and KE_y, respectively, in J m⁻² s⁻¹) along with their vector sum (KE_r, in J m⁻² s⁻¹) explained the variation in D. Neither sand size nor sand moisture was statistically significant alone although binary interactions of KE_r, KE_x and KE_y with the sand size and three-way interaction of KE_x, sand size and moisture were statistically significant. These results can be explained by size-dependent variation in sand compressibility and surface friction related to the total stress field developed by a given partition of shear and compressive stresses of wind-driven oblique raindrops (KE_x/KE_y). Further analysis of the variation of the unit sand detachment rate (D_u = D/KE_r = g J⁻¹) with rain inclination (α, in degrees) better revealed the effect of WDR obliquity on D_u that further changed with sand size class and moisture state. Finally, the difference in the resulting stress field differentiable by the oblique raindrop trajectories of the experiment over sand surface significantly affected the non-cohesive particle detachment rates, to some extent interacted with size-dependent compressibility and interface shear strength of sand grains.     

Sand transport under increased lateral jetting of raindrops induced by wind

Wind tunnel experiments for ‘Raindrop Detachment and Wind-Driven Transport’ (RD–WDT) process were conducted under improved lateral jetting induced by wind velocities of 6.4, 10, and 12 m s^− 1 at nozzle operating pressures of 75, 100, and 150 kPa. Wind-driven rainfalls were also incident on the windward and leeward slopes of 4° and 9° to have a broad variation in the angle of incidence. The objective of this experimental set-up was to distinguish the roles of both impact components of obliquely striking wind-driven raindrops on RD and wind on WDT. Raindrop impact components and reference horizontal wind were quantified by normal (E_tz) and horizontal (E_tx) kinetic energy fluxes and wind shear velocity (u), respectively, to physically model the process of RD–WDT. The results showed, at each level of u, differential sand transport rates by RD–WDT (q_m(RD–WDT)) occurred depending on the magnitude of raindrop impact components, and q_m(RD–WDT) increased as the relative contribution of E_tz increased. Although E_tx was more correlated with q_m(RD–WDT) than E_tz, the extreme increases in E_tx at the expense of E_tz brought about no increases but decreases in q_m(RD–WDT). An RD–WDT model was built under the process of examining the discrete effects of E_tz and E_tx on RD together with u and resulted in a better coefficient of determination (R² = 0.89) than only total kinetic energy (E_t) did alone with u (R² = 0.84). In this study, E_tx was strongly related to u and not to E_tz, which was the principal difference from the previous rainsplash studies, which relied on the compensatory lateral jet development by the compressive pressure build-up at the raindrop–soil interface. Including E_tx in the RD–WDT model both separated the distinct role of each raindrop impact component in RD and improved the performance of u in WDT by better distinguishing its interaction with E_tx, which was not explicitly separated in previous models of RD–WDT.     

Use of USLE/GIS technology integrated with geostatistics to assess soil erosion risk in different land uses of Indagi Mountain Pass—Çankırı, Turkey

The universal soil loss equation (USLE) is an erosion model to estimate average soil loss that would generally result from splash, sheet, and rill erosion from agricultural plots. Recently, use of USLE has been extended as a useful tool predicting soil losses and planning control practices by the effective integration of the GIS-based procedures to estimate the factor values on a grid cell basis. This study was performed for five different lands uses of Indağı Mountain Pass, Cankırı to predict the soil erosion risk by the USLE/GIS methodology for planning conservation measures in the site. Of the USLE factors, rainfall-runoff erosivity factor (USLE-R) and topographic factor (USLE-LS) were greatly involved in GIS. These were surfaced by correcting USLE-R site-specifically using DEM and climatic data and by evaluating USLE-LS by the flow accumulation tool using DEM and watershed delineation tool to consider the topographical and hydrological effects on the soil loss. The study assessed the soil erodibility factor (USLE-K) by randomly sampled field properties by geostatistical analysis. Crop management factor for different land-use/land cover type and land use (USLE-C) was assigned to the numerical values from crop and flora type, canopy and density of five different land uses, which are plantation, recreational land, cropland, forest and grassland, by means of reclassifying digital land use map available for the site. Support practice factor (USLE-P) was taken as a unit assuming no erosion control practices. USLE/GIS technology together with the geostatistics combined these major erosion factors to predict average soil loss per unit area per unit time. Resulting soil loss map revealed that spatial average soil loss in terms of the land uses were 1.99, 1.29, 1.21, 1.20, 0.89 t ha⁻¹ year⁻¹ for the cropland, grassland, recreation, plantation and forest, respectively. Since the rate of soil formation was expected to be so slow in Central Anatolia of Turkey and any soil loss of more than 1 ton ha⁻¹ year⁻¹ over 50–100 years was considered as irreversible for this region, soil erosion in the Indağı Mountain Pass, to the great extent, attained the irreversible state, and these findings should be very useful to take mitigation measures in the site.     

On the application of a particle dispersion model

This paper is concerned with the modeling of particle transport at the Safaniya sea area. It presents the modeling aspects of a marine environment impact study at the Safaniya offshore facility. The offshore facility has continuous discharges of hypochlorite concentration, sanitary waste water, oily water, brine, and sea cooling water. The dispersion of pollutants in the Safaniya sea area is analyzed with the aid of a particle dispersion model. The dispersion of a continuous discharge from the offshore platform is simulated for typical meteorological conditions during the seasons of winter, spring, summer, and fall. Maximum average pollutant concentrations are obtained at various depths. A time series of pollutant concentration near the location of the discharge is constructed. The sea areas affected by the discharge are computed. The dispersion of a hypochlorite concentrate with concentration of 2 ppm is analyzed. Results indicate that the average chlorine concentration has a maximum of 0.27 × 10⁻² ppm.     

Sand detachment by wind‐driven raindrops

Wind movement and velocity can have a profound effect on some aspects of the soil erosion process. In the case of wind‐driven rain, differences in raindrop trajectory are expected: wind‐driven raindrops achieve some degree of horizontal velocity, which increases their resultant impact velocity and they strike the soil surface at an angle deviated from the vertical under the effects of both gravitational and drag forces. However, not much is known about the physical impact of raindrops on a soil in situations where this impact is at an angle, and it is also not precise known if oblique raindrops have stronger erosive effects than vertical ones. A series of tests was conducted to assess the effect of wind velocities on sand detachment from splash cups in a wind tunnel facility equipped with a rainfall simulator. Splash cups packed with standard sand were exposed to windless rains and to rains driven by horizontal wind velocities of 6, 10 and 14 m s^?1 to evaluate the sand detachment by wind‐driven raindrops. The average angle of rain inclination from vertical was calculated from the direct intensity measurements implemented with windward and leeward‐facing raingauges placed at different slopes. A kinetic energy sensor measured energy of windless and wind‐driven rains. Results showed that the kinetic energy flux calculated by the resultant impact velocity of drops adequately described the sand detachment from the splash cups by wind‐driven raindrops. However, an additional analysis of Pearson correlation coefficients using the velocity components rather than the resultant velocity of wind‐driven raindrops indicated that the energy flux related to the horizontal component of wind‐driven raindrops had a greater correlation with sand detachment than that related to the normal component. This finding contradicted the general assumption that the component of velocity normal to the surface is related to the detachment. Copyright © 2005 John Wiley & Sons, Ltd.     

Modeling aggregate size distribution of eroded sediment resulting from rain-splash and raindrop impacted flow processes

Soil susceptibility to detachment and transport sub-processes of erosion is generally controled by the aggregate breakdown mechanism. Measuring particle size and aggregation to the estimate erodibility potential of soils is important under erosive rainfall conditions. The Aggregate Size Distribution (ASD) is one of the most important determinants of soil structure along with soil organic matter content for describing the efficiency of applied, sustainable management strategies. This study aimed to compare the performances of three different aggregate size distribution models to predict the characteristic aggregate size parameter (median diameter, D50) for eroded sediment from interrill erosion processes of Rain- Splash Transport (RST) and Raindrop Impacted Flow Transport (RIFT). The ASDs of 1143 collected sediment samples from the RST and RIFT processes were measured and modeled by the Log-normal, Fractal, and Weibull approaches. The D50 value, as a characteristic parameter for aggregate size distributions, derived from the cumulative ASD curve was compared for soils from different land use types and different slope and rainfall intensity conditions. The performance of each model was evaluated using the Mean Square Error (MSE) and Coefficient of Determination (R^2). The Weibull approach was the most accurate model showing the best fit with the lowest MSE values (0.0002 ≤MSE≤ 0.0048) and having the greatest R2 values (0.936≤ R^2≤ 0.998) when compared with the Log-normal and Fractal models. Herewith, for semi-arid land use and soil, specific shape and scale parameters for the Weibull distribution, the respective ASDs were successfully re-generated for modeling the eroded sediment of the simulated RST and RIFT interill processes.     

Building a semantic based public transportation geoportal compliant with the INSPIRE transport network data theme

Interoperability is becoming essential for the today’s geographic information systems. Geographic information is usually available as datasets stored in databases and accessible via GIS. However, these information sources are increasingly heterogeneous and show differences in data formats, database schema and object concepts. To satisfy the increased demand for the use and sharing of geographic data in common applications, considering the heterogeneity and the methods to support interoperability are required by the GIS community. The implementation of Spatial Data Infrastructure (SDI) such as the European INSPIRE (Infrastructure for Spatial Information in the European Community) enables accessibility and the sharing of geographic data and interoperability among the systems. In addition to this, traditional GIS systems perform spatial queries using a keyword-based method. However, this approach remains incapable of fully expressing the users' needs due to a lack of geographic concepts (semantics) in the dataset. Different terms may refer to similar concepts, while the same terms may refer to different concepts. This causes semantic heterogeneity in the dataset. In this context, the most promising approach is the implementation of geospatial semantics by means of ontology in the geospatial dataset to overcome this kind of ambiguity. The aim of this research is to investigate the implementation of INSPIRE as a SDI standard and the use of Semantic Technology to empower the traditional GIS approach. In this regard, a public transportation geoportal has been developed for the experimental investigation which uses a revised sample transportation data complaint with the INSPIRE Transport Network Data Theme and a developed Transportation Ontology Domain, including concepts, relationships and individuals to provide a semantic spatial search.     

Mechanics of interrill erosion with wind‐driven rain

The vector physics of wind‐driven rain (WDR) differs from that of wind‐free rain, and the interrill soil detachment equations in the Water Erosion Prediction Project (WEPP) model were not originally developed to deal with this phenomenon. This article provides an evaluation of the performance of the interrill component of the WEPP model for WDR events. The interrill delivery rates were measured in the wind tunnel facility of the International Center for Eremology (ICE), Ghent University, Belgium with an experimental setup to study different raindrop impact velocity vectors. Synchronized wind and rain simulations with wind velocities of 6, 10 and 14 m s^–1 were applied to a test surface placed on windward and leeward slopes of 7, 15 and 20%. Since both rainfall intensity and raindrop impact velocity varied greatly depending on differences in the horizontal wind velocity under WDRs, the resultant kinetic energy flux (KE_r, in J m^–2 s^–1) was initially used in place of the WEPP model intensity term in order to incorporate the effect of wind on impact velocity and frequency of raindrops. However, our results showed only minor improvement in the model predictions. For all research data, the model Coefficients of Determination (r²) were 0·63 and 0·71, when using the WEPP and the KE_r approaches, respectively. Alternately, integrating the angle of rain incidence into the model by vectorally partitioning normal kinetic energy flux (KE_rn, in J m^–2 s^–1) from the KE_r greatly improved the model's ability to estimate the interrill sediment delivery rates (r² = 0·91). This finding suggested that along with the fall trajectory of wind‐driven raindrops with a given frequency, raindrop velocity and direction at the point of impact onto the soil surface provided sufficient physical information to improve WEPP sediment delivery rate predictions under WDR. Copyright © 2012 John Wiley & Sons, Ltd.